Federalism is a combined and compound mode of government that combines a general government (the central or "federal" government) with regional governments (provincial, state, cantonal, territorial, or other sub-unit governments) in a single political system, dividing the powers between the two. Federalism in the modern era was first adopted in the unions of states during the Old Swiss Confederacy.

Federalism differs from confederalism, in which the general level of government is subordinate to the regional level, and from devolution within a unitary state, in which the regional level of government is subordinate to the general level. It represents the central form in the pathway of regional integration or separation, bounded on the less integrated side by confederalism and on the more integrated side by devolution within a unitary state.

Examples of a federation or federal province or state include Argentina, Australia, Belgium, Bosnia & Herzegovina, Brazil, Canada, Germany, India, Iraq, Malaysia, Mexico, Micronesia, Nepal, Nigeria, Pakistan, Russia, Switzerland, the United Arab Emirates, and the United States. Some characterize the European Union as the pioneering example of federalism in a multi-state setting, in a concept termed the "federal union of states".